Magnetic field coil for concentrating the arc in a vacuum arc furnace



2,978,525 ING H. GRUBER ET AL MAGNETIC FIELD COIL FOR CONCENTRAT Filed June 6, 1958 THE ARC IN A VACUUM ARC FURNAC April 4, 1961 MAGNETIC FIELD COIL FOR CONCENTRATING THE ARC IN A VACUUM ARC FURNACE Helmut Gruber and Helmut Scheidig, Hanan (Main), Germany, assignors to W. C. Heraeus G.m.b.H., Hanan (Main), Germany, a corporation of Germany The present invention relates to improvements in a vacuum arc furnace for melting metals.

It has for some time been conventional to provide vacuum arc furnaces with magnetic field coils for con centrating the arc and for preventing it from deviating from the desired area within which the melting process is to be carried out and thus, for example, for preventing the are from moving over to the water-cooling jacket of the crucible where it could easily burn through the material and cause the water to enter into the vacuum chamber. Such field coils are also used for agitating the bath of molten metal in order to homogenize it. This is especially of importance in those cases in which an alloy of two or more metals is to be produced.

Prior to this invention, such field coils were simply wound around the outside of the water jacket of the crucible. However, it has now been found that such manner of mounting the field coil has the disadvantage that it is spaced at a considerable distance from the arc and that therefore the magnetic field will be rather weak Within the area of the arc.

It is an object of the present invention to provide such a field coil in a position so as to overcome the abovementioned disadvantages. This object may, according to the invention, be attained by mounting the field coil within the water-cooling jacket of the crucible, and preferably by Winding it directly upon the crucible so that it will then be located more closely to the arc and be water-cooled.

Since the coil will thus be cooled by the water circulation which cools the crucible, a current of a much higher intensity may be passed through it without requiring any increase in the thickness of the wire. Furthermore, the coil will then be as close to the are as possible and will therefore produce a much stronger magnetic field than hitherto possible with a current of the same amperage and the same number of coil windings. The outer wall of the cooling jacket will then also not require to be made of any expensive nonmagnetic material. Consequently, the improvement according to the present invention will result in a substantial reduction of the cost of manufacture of an arc furnace of the mentioned type.

These and other objects, features, and advantages of the present invention will become more apparent from the following detailed description thereof, particularly when read with reference to the accompanying drawing which diagrammatically illustrates in cross section an arc furnace which is provided with a field coil according to the invention.

Referring to the drawing, the upper part of the furnace 1 has a suitable duct 2 through which an electrode suspension rod 3 is inserted which carries a consumable electrode 4 at its lower end. A pipe 5 connects the furnace to a pump unit, not shown, for evacuating the inside of the furnace.

A crucible 6 is adapted to be mounted on the upper part of the furnace and is then sealed toward the outer United States Patent 0 Patented Apr. 4, 1961 atmosphere by means of a sealing ring 7. Crucible 6 is adapted to contain the ingot 8 which is produced by melting of the electrode 4 by means of the are 9.

Crucbile 6 consists of an inner wall -6 and an outer wall 10. The intervening space between walls 6' and 10 forms a water jacket 10. A field coil 11 is wound directly upon the inner wall 6' of crucible 6 and is thus located within the water jacket 10. However, the individual coil windings are spaced at such a distance from each other that the cooling effect of the water upon the crucible will not be materially reduced by the presence of the coil on the inner wall 6.

The two conductors 12 and 13 for supplying the electric current to field coil 11 are provided with a watertight insulation and extend through the outer wall 10' and the water jacket 10.

Contrary to the prevailing opinion it has been found that a field coil as above described may be easily insulated from the water within water jacket 10, for example, by being provided with an enamel coating of synthetic resins. When using a lower operating voltage, it is also possible to avoid an electrolysis of the cooling water. This may especially be attained according to the invention because the field coil will be cooled by the water and will therefore admit the use of a current of a high amperage. Because of the short distance between the arc and the field coil which surrounds the crucible along almost its entire length, this coil may also be subdivided into several shorter coil sections of which only that section has to be used which surrounds the are at its particular level which gradually rises toward the top of the crucible in accordance with the gradual increase in the size of the ingot. Suitable control means may then be provided for energizing one or more of the dilferent coil sections successively. As shown in the drawing, one suitable way of sudividing the coil into several short coil sections includes an upper intermediate conductor 16 connected to one of the turns a relatively short distance from the upper end of the coil, and a lower intermediate conductor 18 connected to one of the turns a relatively short distance from the lower end of the coil. A first switch 20 is connected to a first terminal 21 of a power source 22. A second switch 23 is connected to a second terminal 24 of the power source. Switch 20 is adapted to connect conductors 13, 16, or 18 to the first terminal of the power supply, and switch 23 is adapted to connect conductors 12, 16, or 18 to the second terminal of the power supply. As is obvious from the drawing, by suitably positioning the switches, any individual group, or combination of groups of coil turns lying between adjacent conductors, can be energized, or all turns of the coil can be energized.

Although our invention has been illustrated and described with reference to the preferred embodiments thereof, we wish to have it understood that it is in no way limited to the details of such embodiments, but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed our invention, what we claim is:

1. A vacuum arc furnace comprising an upper furnace part, a crucible adapted to be connected to said upper part, an electrode within said upper part and adapted to extend into said crucible, means for evacuating said upper part and said crucible, a field coil wound around the outside of said crucible in direct contact with it for stabilizing said are, and water-cooling means for cooling said coil and crucible.

2. A vacuum arc furnace comprising an upper furnace part, a crucible adapted to be connected to said upper part, an electrode within said upper part and adapted to extend into said crucible for producing an electric are therein, means for evacuating said upper part and said crucible, a Water jacket around the outside of said crucible, means for circulating cooling water through said water jacket, vand a field coil within the chamber formed by said Water jacket for stabilizing said arc, said coil being wound around the outside of said crucible in direct contact with it and when energized constructed and arranged to be cooled by said cooling water.

3. A vacuum arc furnace as defined in claim 2, wherein said field coil is divided into a plurality of sections, and further comprising means for selectively energizing said sections.

4. Apparatus according to claim 2 in which adjacent turns of the coil are spaced from each other to leave open spaces through which water in the jacket can make direct contact with the outside of the crucible.

References Cited in the file of this patent UNITED STATES PATENTS 133,099 Hay Nov. 19, 1872 1,840,247 Northrup Jan. 5, 1932 1,943,802 Northrup Jan. 16, 1934 2,727,936 Boyer Dec. 20, 1955 2,727,937 Boyer r Dec. 20, 1955 Laird et a1. Aug. 28, 1956 

